1. Field of the Invention
The present invention relates generally to knee replacement procedures and, more particularly, to methods of minimally invasive unicompartmental knee replacement.
2. Brief Description of the Related Art
Prosthetic knee joint components are increasingly used to repair knee joints damaged by trauma and/or disease. Basically, the natural knee joint includes an upper or proximal part of the tibia, constituted by the medial and lateral tibial plateaus, a lower or distal part of the femur, constituted by the medial and lateral femoral condyles, and menisci between the tibial plateaus and the femoral condyles along with the patella which covers the anterior surface of the knee. The type of prosthesis implanted in the knee must be matched to the needs of the patient and may involve total knee replacement or arthroplasty in which both femoral condyles and both tibial plateaus are surgically restored using appropriate femoral and tibial prosthetic components. Depending on the particular patient, unicompartmental or partial knee replacement or arthroplasty may be preferable to total knee replacement and involves implantation of femoral and tibial prosthetic components on either the medial or lateral portion of the tibial-femoral joint while preserving more of the normal remaining anatomical structure in the knee. Both total and unicompartmental knee joint replacement procedures involve preparing the bone surfaces of the femoral condyle and the tibial plateau to receive the corresponding prosthetic components. It is very important in both total and unicompartmental knee joint replacement procedures that the bone surfaces be prepared accurately and at the proper location to ensure that the implanted prosthetic components achieve replication as close as possible to the natural knee joint.
Where unicompartmental knee replacement is preferable to total knee replacement, it is desirable that unicompartmental knee replacement be accomplished with minimal bone removal so that sufficient bone remains for potential future surgical intervention, such as future total knee replacement. Unicompartmental knee replacement may be a viable interim procedure to delay the need for a total knee replacement in many patients, since it is easier to later revise a unicompartmental knee replacement to a total knee replacement than it is to revise a total knee replacement to another total knee replacement. Other advantages of unicompartmental knee replacement over total knee replacement include easier recuperations and quicker recovery times for patients, decreased hospital stays, elimination of the need for formal physical therapy in many patients after hospital discharge, retention of the cruciate ligaments, preservation of nearly normal kinematics, and use of minimally invasive incisions to access the operative site.
Unfortunately, conventional unicompartmental knee replacement techniques are very technically demanding and the instrumentation and prostheses used in conventional unicompartmental knee replacements have various drawbacks such that reproducible clinical results are difficult to attain. Many conventional unicompartmental knee replacement procedures and instrumentation involve relatively large incisions with significant exposure, greater intramedullary invasiveness, poor alignment and reproducibility, and/or inaccurate bone preparation. The instrumentation used in many prior unicompartmental knee replacement procedures is inapplicable to minimally invasive surgery. Unicompartmental knee replacement systems designed for minimal exposure have historically provided limited instrumentation, making reproducible alignment difficult, or bulky instrumentation, which requires more intrusive surgery. Furthermore, conventional unicompartmental knee replacement procedures typically involve significant bone removal such that quality bone must be unduly sacrificed.
Various instruments have been proposed for use in knee replacement procedures to provide alignment and/or bone cutting for femoral and tibial bone preparation. Such instruments are represented by U.S. Pat. No. 4,502,483 to Lacey, U.S. Pat. Nos. 4,524,766 and 4,567,886 to Petersen, U.S. Pat. No. 4,574,794 to Cooke et al, U.S. Pat. No. 4,718,413 to Johnson, U.S. Pat. No. 4,773,407 to Petersen, U.S. Pat. No. 4,787,383 to Kenna, U.S. Pat. No. 4,926,847 to Luckman, U.S. Pat. No. 5,098,436 to Ferrante et al, U.S. Pat. No. 5,100,409 to Coates et al, U.S. Pat. No. 5,122,144 to Bert et al, U.S. Pat. Nos. 5,171,244 and 5,228,459 to Caspari, U.S. Pat. No. 5,234,433 to Bert et al, U.S. Pat. Nos. 5,263,498 and 5,304,181 to Caspari et al, U.S. Pat. No. 5,312,411 to Steele et al, U.S. Pat. No. 5,395,376 to Caspari et al, U.S. Pat. No. 5,520,695 to Luckman, U.S. Pat. No. 5,569,259 to Ferrante et al, U.S. Pat. No. 5,662,656 to White, U.S. Pat. No. 5,709,689 to Ferrante et al, U.S. Pat. No. 6,059,831 to Braslow et al, and U.S. Pat. No. 6,102,954 to Albrektsson et al, the Biomet Repicci II, the MIS Minimally Invasive Solution of Zimmer, Inc., and the Johnson & Johnson P.F.C. In many cases, femoral preparation involves forming a plurality of planar angled or chamfered resections. The Braslow et al and Luckman '695 patents are, for example, illustrative of this type of femoral preparation. The need to implement a plurality of planar angled cuts in the femur in order to accommodate the prosthetic femoral component is disadvantageous for the relatively large quantity of bone that must be removed. U.S. Pat. No. 4,719,908 to Averill et al describes contouring the femur using a cutter and a contouring guide to obtain a contour that minimizes the amount of bone removed from the femoral condyle. However, placement of the contouring guide depends for accuracy on the location of holes previously formed in the condyle to receive fixation posts of the femoral component.
The Biomet Repicci II, the MIS Minimally Invasive Solution of Zimmer, Inc., and the Johnson & Johnson P.F.C. relate to unicompartmental knee replacement procedures and instrumentation but present various disadvantages. The Biomet Repicci II knee replacement procedure lacks alignment instrumentation and requires a completely freehand burring technique to shape the femoral condyle. In addition, a pegless tibial base must be placed completely in a pocket of the cancellous bone. The MIS knee replacement procedure involves full femoral and tibial resections, incorporates a difficult implantation technique and requires invasive intramedullary alignment. The Johnson & Johnson P.F.C. knee replacement procedure fails to provide minimally invasive instrumentation and requires full femoral and tibial resections.
Accordingly, the need exists for instruments and methods for unicompartmental knee replacement which provide a conservative approach in terms of bone removal and exposure while providing consistent alignment and reproducible clinical results in a minimal incision technique. There is a need for better instrumentation and for a unicompartmental knee replacement procedure utilizing such instrumentation in a minimally invasive technique while providing the alignment needed to produce consistent, repeatable outcomes.